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Serum, lymphocyte and erythrocyte potassium, magnesium and calcium concentrations were measured in 31 patients with congestive cardiac failure and 14 patients with mild noncomplicated hypertension, who had been receiving either furosemide or chlorothia-zide (with or without potassium supplementation) or a combination of hydrochlorothiazide and amiloride for more than 6 months. Lymphocyte potassium concentrations (pmol/l00 cells ± SE) were as follows: controls 18.1 ± 1.5, furosemide 14.1 ± 0.9 (p < 0.001), furosemide + potassium 12.3 ± 0.7 (p < 0.001), chlorothiazide 13.1 ± 1.0 (p < 0.001) and hydrochlorothiazide + amiloride 18.6 ± 0.7 (p = NS). There was a statistically significant relationship between the number of months the patients had been on diuretics and their lymphocyte potassium concentrations. Serum electrolytes, apart from the group receiving chlorothiazide who showed a significant fall in serum K, were unchanged.

In 18 patients with gastrointestinal manifestations of digoxin toxicity the mean serum digoxin concentration (+ SEM) was 3 16 ,tg/l (± 0-25), the calcium to potassium ratio 0 31 (±0 01), and the mean arterial pH 7 406 (4-0017). In contrast 19 patients with digoxin induced automaticity had a mean serum digoxin concentration of 124 [tg/l ( 0-15; p<0001), a calcium to potassium ratio of 038 (±001; p<001), and an arterial pH of 7498 (I 0008; p <0001). Eight out of 13 patients with digoxin induced cardiotoxicity had serum concentrations of the drug within the therapeutic range (0-8-2-0 tg/l). The calcium to potassium ratio, however, was lower than in the patients with automaticity (0 31±0 02; p<0 01) and the arterial pH was 7-370 (±0 033; p<0 05). Serum magnesium concentrations were similar in all groups.In this study patients with digoxin induced gastrointestinal symptoms had high serum concentrations of the drug, whereas those with drug induced automaticity had therapeutic concentrations. This second group, however, was identified by their higher calcium to potassium ratios and higher pH values.

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